The present invention relates to devices that require periodic maintenance such as involving calibration, more particularly to methods for systematically applying maintenance procedures to groups of such devices.
Four traditional maintenance strategies are “reactive” maintenance (also known as “run-to failure” maintenance), “preventive” maintenance (also known as “interval,” “cycle-based,” or “time-based” maintenance), “predictive” maintenance (also known as “condition-based” maintenance), and “proactive” maintenance. Reactive maintenance is most suitable for small or unimportant items or those that are redundant or unlikely to fail. Preventive maintenance is particularly appropriate for items that are subject to wearing out or those having a known pattern of failure. Predictive maintenance is considered to be superior to the other strategies when the item has a random pattern of failure, or is not subject to wearing out, or would be subject to failure induced by preventive maintenance were it implemented. Proactive maintenance usually involves root cause failure analysis (RCFA) or failure modes and effects analysis (FMEA).
In recent years a maintenance strategy known as “reliability centered” maintenance (RCM) has come into prominence. RCM seeks to optimally combine the four aforementioned strategies so as to take advantage of the respective strengths of each, thereby maximizing operability and efficiency of equipment and facilities while minimizing life-cycle costs. Essentially, RCM involves the integration of the four aforementioned strategies whereby actions are identified in order to increase cost-effectiveness and reduce probability of failure. The RCM process determines the maintenance requirements of any physical entity in the context of its operation, the overall goal basically being the provision of the required operation performance at the lowest cost. Implicit in RCM is its recognition that the various types of equipment in a typical operation will generally differ in terms of their importance as well as their failure probabilities and mechanisms. RCM analysis typically lends itself to formulation of a “decision logic tree” wherein equipment is considered with regard to (i) function, (ii) likely functional failures, (iii) likely consequences of functional failures, and (iv) action that can be taken to reduce the probability or consequences of failure, or to identify the onset of failure.
The U.S. Navy's customary method for conducting instrument calibration requirements analysis is pursuant to the Shipboard Instrumentation and Systems Calibration (SISCAL) program, which uses a logic tree almost identical to the “Calibration Decision Logic Tree” published in the Joint Fleet Maintenance Manual (JFFM, CINCLANTFLT/CINCPACFLTINST 4790.3) at Volume VI, Chapter 9, Appendix B-1 (formerly found at Volume IV, Chapter 12, Appendix C-1). The JFFM's Calibration Decision Logic Tree does not reflect reliability-centered maintenance (RCM) principles; in particular, it neither addresses installed instrument applications, nor considers appropriate instrument tolerances, nor considers maintenance actions alternative to calibration.